The evolution from azide-based gas generants to nonazide gas generants is well-documented in the prior art. The advantages of nonazide gas generant compositions in comparison with azide gas generants have been extensively described in the patent literature, for example, U.S. Pat. Nos. 4,370,181; 4,909,549; 4,948,439; 5,084,118; 5,139,588 and 5,035,757, the discussions of which are hereby incorporated by reference.
In addition to a fuel constituent, pyrotechnic nonazide gas generants contain ingredients such as oxidizers to provide the required oxygen for rapid combustion and reduce the quantity of toxic gases generated, a catalyst to promote the conversion of toxic oxides of carbon and nitrogen to innocuous gases, and a slag forming constituent to cause the solid and liquid products formed during and immediately after combustion to agglomerate into filterable clinker-like particulates. Other optional additives, such as burning rate enhancers or ballistic modifiers and ignition aids, are used to control the ignitability and combustion properties of the gas generant.
One of the disadvantages of known nonazide gas generant compositions is the amount and physical nature of the solid residues formed during combustion. When employed in a vehicle occupant protection system, the solids produced as a result of combustion must be filtered and otherwise kept away from contact with the occupants of the vehicle. It is therefore highly desirable to develop compositions that produce a minimum of solid particulates while still providing adequate quantities of a nontoxic gas to inflate the safety device at a high rate. With regard to nontoxic gas, it is desirable to reduce or eliminate certain gaseous species including nitrogen oxides.
Known pyrotechnic non-azide gas generants sometimes are disadvantaged by generating relatively higher levels of CO, NH3, NO, and NO2. The oxygen balance can be adjusted to minimize either CO, or NO and NO2. However, if CO is low then NO and NO2 will typically be relatively high. On the other hand, if NO and NO2 are low, then CO will typically be relatively high. Accordingly, there is a need for a gas generant composition that forms low levels of these gases.
Yet another concern includes sustaining combustion with regard to gas generating compositions used in linear inflators, or inflators employed for rollover or head curtain application. Certain compositions including perchlorate salts and nonmetallic fuels are desirable. However, one challenge with these types of compositions is to improve combustion propagation throughout the length of the inflator, such as a linear inflator typically employed as a rollover or head curtain cushion. Another concern is to reduce the relative hygroscopicity of these gas generants.
Accordingly, ongoing efforts in the design of automotive gas generating systems, for example, include other initiatives that reconcile the need for reasonable amounts of gas produced the drawbacks mentioned above.